A machine for cutting hard surfaces has a rotatable member such as a wheel or a drum which turns about an axis and has a plurality of cutting tools mounted on the rotatable member. To advance the cut, the rotating member is applied against the hard surface such that each tool removes a small portion of hardened material.
To maximize their useful life, the cutting tools are rotatably mounted about a longitudinal axis and have a cylindrically mounted portion rotatably fitted in a cylindrical aperture on a mounting block on the rotating member. To transfer force from the mounting block to the tool, the tool is provided with an annular flange having a planar rear surface which rests upon the planar forward surface of the mounting block surrounding the aperture such that the forward surface of the mounting block applies force to the rear surface of the flange.
Each of the tools also has a tapered forward cutting end with a tungsten carbide insert at the forward end thereof for cutting into the hard surfaces. As the machine cuts hard material, such as concrete or asphalt, fragments of the broken material are forced across the tapered forward end of the tool and around the sides of the mounting block causing wear, or wash away, of the material which make up both the tool body and the mounting block. After a substantial portion of the forward end of the tool has been worn away, the tool must be replaced. Similarly, after a substantial portion of the mounting block has been washed away, the mounting block must also be replaced.
A recent improvement in such machines is a quick-change assembly wherein the cylindrical shank of the tool is received in a tubular retainer. The tubular retainer is then fitted into a mounting block on the machine. In this configuration, it is the tubular retainer and not the mounting block which suffers wash away when the machine is in use. The tubular retainer can be more easily replaced than the block into which it is mounted, thereby simplifying the repair of the machine.
Other improvements have also enhanced the life of the mounting block. For example, the radial flanges of the tools have been enlarged to protect the block from damage caused by wash away. In my co-pending application Ser. No. 09/505,088, 1 also disclosed a tungsten carbide insert provided at the forward end of the mounting block to reduce the damage to the block caused by the rotation of the tool within the cylindrical bore. As a result of such improvements, as many as one hundred tools may be worn out before a mounting block suffers such wear that it, too, must be replaced.
The tools used in such machines are symmetric about their longitudinal axis and the rotation of the tool within the cylindrical mounting causes the tool body to wear evenly around its circumference. Even so, such tools become worn very rapidly and it is common to replace all of the tools on a machine after a single day of usage. A tool which does not rotate properly, however, will fail prematurely and the failure of several tools on a machine can cause the machine to be taken out of service before completion of a day's work. Proper rotation of the tools is, therefore, essential for operating the machine efficiently.
It has become common to provide a washer around the circumference of the tool shank such that the washer is positioned between the forward surface of the tool body and the flange of the tool. The washer is made of a hardened steel and has a polished surface which acts as a bearing on which the rear surface of the flange is rotatable thereby enhancing tool rotation. When a tool becomes worn, both the tool and the washer are removed from the mounting block for the tool retainer and replaced with a new tool and a new washer.
Certain new problems are created, however, by the provision of a washer. For example, the tools have a frustoconical portion between the shank and the rearward surface of the flange and, therefor, the washer must have an inner diameter equal to the largest diameter of the frustoconical portion. If the washer is not properly centered on the tool while it is being inserted into the retainer or tool block, the washer will prevent the tool from being properly seated in its holder. An improperly seated tool will not rotate properly, and will contribute to the premature failure of the tool holder.
To operate properly, the washers in such assemblies are to remain stationary with respect to the tool holder and not rotate with the tool. Where the tool holder is provided with a polished forward surface, the washer may tend to rotate with the tool and thereby defeat its purpose. Where the tool holder is fitted with a tungsten carbide ring at the forward end therefore, such as disclosed in my co-pending application Ser. No. 09/505,088, there is a high likelihood that the washer will rotate with the tool because the tungsten carbide of the ring has a lower coefficient of friction than does the steel of the washer. It is desirable, therefore, to provide a method for facilitating the centering of the washer with respect to the tool and for retaining the washer stationary with respect to the tool holder and against rotation with the tool.